I'm pretty sure the article resolves the implicit dependencies at the point of the declaration. (Did I misunderstood it?)

So, you don't have a `data HashMap datatype`, you have a `data HashMap hashAlgo datatype`, where hashAlgo is decided implicitly by the context. That's the entire reason it's called "implicit".

Every other usage of the data knows how to hash your values because of that `hashAlgo` parameter. It doesn't matter where it happens.